As this type of flat storage facility, for example, as disclosed in Japanese Published Unexamined Patent Application No. 2008-262276 (Patent Literature 1), a flat storage facility has been known which includes a storage item placement plane and a storage/retrieval device, in which the storage/retrieval device includes a Y-direction laterally moving member that is freely moved horizontally and laterally in a Y direction at a certain height above the storage item placement plane, a carriage that is freely moved horizontally in an X direction perpendicularly intersecting the Y direction above the Y-direction laterally moving member, and a storage item gripping means that is provided in the carriage so as to be freely raised and lowered, and in which the storage/retrieval device is configured so as to perform storage/retrieval on a storage item between respective storage item placement points set on the storage item placement plane.